A sonication extraction method for the analysis of pyrethroid, organophosphate, and organochlorine pesticides from sediment by gas chromatography with electron-capture detection.

A method was developed for the simultaneous determination of 5 pyrethroid, 1 organophosphate, and 20 organochlorine pesticides in sediment. Pesticide residues were extracted using sonication with acetone-methylene chloride (1:1 vol/vol) and the extracts were subsequently cleaned with deactivated Florisil (magnesium silicate; U.S. Silica, Berkeley Springs, West Virginia). Gas chromatography with an electroncapture detector was used for analyte determination, and two columns were used for confirmation of the analytes. Four control sediments from different sources were spiked with a pesticide mix and analyzed for method validation. The method detection limits ranged from 0.22 to 0.85 microg/kg dry sediment. Recoveries for spiked samples at four concentrations (1, 5, 20, and 400 microg/kg dry sediment) were 71.9% to 129.8% with relative standard deviations (RSDs) < 11%. Taking the matrix effect into account, 1 microg/kg was chosen for the threshold of detection, but 0.5 microg/kg of spiked control sediment still provided good recoveries and RSDs. This method was validated using field-collected sediment taken from agricultural areas of Fresno County, California.